#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <math.h> 
#include <ctype.h> 
#include <time.h> 
#include <assert.h>

int main()
{
	int n = 20;
	int over = 0;
	while (n)
	{
		n--;
		over++;
		if (over % 2 == 0)
		{
			n++;
		}
	}

	printf("%d\n", over);
	return 0;
}